FIG. 1 shows a schematic view of a fuselage 10 of an aircraft with a central wing box 12 providing the connection between the fuselage and the wings and a landing gear casing 14. For the remainder of the description, longitudinal direction is to be understood as the direction corresponding to the greatest dimension of the fuselage. A transverse plane is a plane that is perpendicular to the longitudinal direction. The front of the aircraft corresponds to the nose of the fuselage and the rear corresponds to the tail unit.
On both sides of the central wing box 12 and/or of the landing gear casing 14, the fuselage 10 comprises a first section 16 arranged at the front and a second section 18 arranged at the rear, the two sections 16 and 18 being connected by a keel beam 20 arranged under the central wing box 12.
According to an embodiment shown in FIG. 2, a keel beam 20 is metallic and has a section substantially rectangular with an upper panel 22.1, a lower panel 22.2, two lateral panels 22.3 and 22.4 connected by angle plates 24 at each angle.
To enable this assembly, the laterals panels 22.3 and 22.4 have openings 26 to enable access to the fastenings located inside the beam.
The fact that the lateral panels have openings necessarily impacts the strength of the beam, which makes it necessary to increase the size of its section for taking up forces.
Alternatively, the elements of the beam are made of composite material. Even if this solution makes it possible to reduce the onboard mass, it does not optimize it considering the geometry of the elements constituting the beam.
According to another drawback, the free edges of the panels forming the beam, particularly those provided in the area of the lower angles, are exposed to the path of tire or rim debris when the landing gear is out. In the case of the panels from composite material, an impact in the area of the side of the panel can have substantial consequences on the mechanical characteristics of the panel.
According to another drawback, the keel beam and the central wing box are connected by means of splice plates which do not allow any slight deformation around an axis, parallel to the longitudinal direction. The rigidity of the connection between the central wing box and the keel beam causes the stresses in the area of the keel beam caused by the flexion forces of the wings to be increased.